N metal for FinFET

ABSTRACT

An N work function metal for a gate stack of a field effect transistor (FinFET) and method of forming the same are provided. An embodiment FinFET includes a fin supported by a semiconductor substrate, the fin extending between a source and a drain and having a channel region, and a gate stack formed over the channel region of the fin, the gate stack including an N work function metal layer comprising an oxidation layer on opposing sides of a tantalum aluminide carbide (TaAlC) layer.

BACKGROUND

Semiconductor devices are used in a large number of electronic devices,such as computers, cell phones, and others. Semiconductor devicescomprise integrated circuits that are formed on semiconductor wafers bydepositing many types of thin films of material over the semiconductorwafers, and patterning the thin films of material to form the integratedcircuits. Integrated circuits include field-effect transistors (FETs)such as metal oxide semiconductor (MOS) transistors.

One of the goals of the semiconductor industry is to continue shrinkingthe size and increasing the speed of individual FETs. To achieve thesegoals, fin FETs (FinFETs) or multiple gate transistors are used in sub32 nm transistor nodes. FinFETs not only improve areal density, but alsoimprove gate control of the channel.

In order to set the threshold voltage (V_(t)) for a FinFET, a workfunction (WF) metal is included in the gate stack. Because the gatestack of the FinFET is formed over both the top and sidewalls of thechannel, a conformal process is needed to form the gate stack.Unfortunately, the physical vapor deposition (PVD) process typicallyused to form the N work function metal (e.g., titanium aluminide, TiAl)for a planar device is not suitable for formation of the gate stack inthe FinFET. Indeed, the physical vapor deposition is not conformal.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates an embodiment FinFET having a gate stack with an Nwork function metal layer including an oxidation layer on opposing sidesof a tantalum aluminide carbide (TaAlC) layer;

FIG. 2 illustrates a line scan energy-dispersive x-ray spectrometry(EDS) graph for a representative slice of the gate stack of FIG. 1;

FIG. 3 illustrates a deposition system that may be utilized to form theN work function metal layer in the gate stack of the FinFET of FIG. 1;

FIG. 4 illustrates an embodiment method of forming N work function metallayer in the gate stack of the FinFET of FIG. 1;

FIG. 5 illustrates a repeating process of pulsing and purging to formmonolayers of the tantalum aluminide carbide (TaAlC) layer in the N workfunction metal layer in the gate stack of the FinFET of FIG. 1;

FIG. 6 illustrates two reaction models illustrating the effect oftemperature in forming the tantalum aluminide carbide (TaAlC) layer inthe N work function metal layer in the gate stack of the FinFET of FIG.1;

FIG. 7 is a chart illustrating the effect of temperature on a flat bandvoltage (V_(fb)) for a FinFET having an N work function metal layerformed from eleven monolayers;

FIG. 8 is a chart illustrating the effect of thickness of the N workfunction metal layer;

FIG. 9 is a chart illustrating the effect of a precursor ratio on a flatband voltage (V_(fb)) for a FinFET having an N work function metal layerformed from eleven monolayers; and

FIG. 10 is a chart depicting various parameters used for the aluminidecarbide (TaAlC) layer composition.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent disclosure provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative, and do not limit thescope of the disclosure.

The present disclosure will be described with respect to preferredembodiments in a specific context, namely a FinFET metal oxidesemiconductor (MOS). The invention may also be applied, however, toother integrated circuits, electronic structures, and the like.

Referring now to FIG. 1, an embodiment FinFET 10 is illustrated. Asshown, the embodiment FinFET 10 includes a fin 12 formed from or on asemiconductor substrate 14. In an embodiment, the semiconductorsubstrate 14 can be recessed to form the fin 12. In an embodiment, thefin 12 can be epitaxially-grown on the semiconductor substrate 14. In anembodiment, the fin 12 and the semiconductor substrate 14 are formedfrom silicon, germanium, silicon germanium, or another suitablesemiconductor material.

As shown in FIG. 1, the fin 12 extends between a source 16 and a drain18 and defines a channel region 20 beneath a gate stack 22. In otherwords, the gate stack 22 is disposed over the channel region 20 of thefin 12. In an embodiment, spacers 24 are supported by the fin 12 anddisposed adjacent to the gate stack 22. In addition, other integratedcircuit structures (e.g., contact plugs to the source 16 and the drain18, an interlevel dielectric (ILD) adjacent the spacers 24, etc.) may beformed in or on the FinFET 10.

Still referring to FIG. 1, the gate stack 22 includes several layers. Inan embodiment, the gate stack 22 includes a gate dielectric layer 26. Asshown, the gate dielectric layer 26 is disposed over the fin 12 abovethe channel region 20. In addition, the gate dielectric layer 26 isdisposed along sidewalls of the spacers 24. In an embodiment, the gatedielectric layer 26 is formed from an interfacial dielectric and ahigh-k dielectric (IL/HK). In an embodiment, the high-k dielectricportion of the gate dielectric layer 26 has a thickness of about 15Angstroms to about 25 Angstroms. Even so, in other embodiments the gatedielectric layer 26 and the high-k dielectric portion of the gatedielectric layer 26 may have other suitable thicknesses.

In an embodiment, a high-k dielectric cap layer 28 is disposed over thegate dielectric layer 26. The high-k dielectric cap layer 28 may beformed from a suitable high-k dielectric material such as, for example,titanium nitride (TiN). In an embodiment, the high-k dielectric caplayer 28 has a thickness of between about 10 Angstroms and about 20Angstroms. Even so, in other embodiments the high-k dielectric cap layer28 may have other suitable thicknesses.

Still referring to FIG. 1, a barrier/etch stop layer (ESL) 30 isdisposed over the high-k dielectric cap layer 28. The barrier/etch stoplayer 30 may be formed from a suitable barrier or etch stop materialsuch as, for example, tantalum nitride (TaN). In an embodiment, thebarrier/etch stop layer 30 has a thickness of about 10 Angstroms toabout 20 Angstroms. Even so, in other embodiments the barrier/etch stoplayer 30 may have other suitable thicknesses.

As shown in FIG. 1, an N work function metal layer 32 is disposed overthe barrier/etch stop layer 30. In an embodiment, the N work functionmetal layer 32 includes an oxidation layer 34 on opposing sides of atantalum aluminide carbide (TaAlC) layer 36. In other words, thinoxidation layers 34 are observed on the surface of the tantalumaluminide carbide layer 36 at the interface of the barrier/etch stoplayer 30 and the N work function metal layer 32 (e.g., TaAlC—TaNinterface) and at the interface of a glue metal layer 38 and the N workfunction metal layer (e.g., TaAlC—TiN interface). As such, in anembodiment the barrier/etch stop layer (ESL) 30 engages with theoxidation layer 34 on an exterior side of the tantalum aluminide carbidelayer 36.

In an embodiment, the N work function metal layer 32 includes about 16%to about 25% aluminum (Al), about 20% to about 29% carbon (C), about 7%to about 16% tantalum (Ta), and about 35% to about 50% oxygen (O). In anembodiment, the ratio of Al/C is about 0.5 to about 1.3, the ratio ofTa/C is about 0.2 to about 0.8, and the ratio of Al/Ta is about 1 toabout 3.6. In an embodiment, a thickness of the N work function metallayer 32 is between about 30 to about 90 Angstroms. Even so, in otherembodiments the N work function metal layer 32 may have other suitablethicknesses. As will be more fully explained below, the tantalumaluminide carbide (TaAlC), which may be referred to as a metal carbidefilm, gives the FinFET 10 of FIG. 1 a tunable work function to meetdevice needs.

Still referring to FIG. 1, the glue metal layer 38 is disposed over theN work function metal layer 32. As such, the glue metal layer 38 engageswith the oxidation layer 34 on an interior side of the tantalumaluminide carbide layer 36. The glue metal layer 38 may be formed from asuitable glue material such as, for example, titanium nitride (TiN). Inan embodiment, the glue metal layer 38 has a thickness of about 10Angstroms to about 30 Angstroms. Even so, in other embodiments the gluemetal layer 38 may have other suitable thicknesses. As shown in FIG. 1,a metal fill layer 40 is disposed over the glue metal layer 38. Themetal fill layer 40 may be formed from a suitable metal such as, forexample, tungsten (W).

Referring now to FIG. 2, a line scan energy-dispersive x-rayspectrometry (EDS) graph 42 is disposed over a representative slice 44of the gate stack 22 of FIG. 1. As the graph 42 of FIG. 2 illustrates,the oxidation layers 34 on opposing sides of the tantalum aluminidecarbide (TaAlC) layer 36 are aluminum (Al) and oxygen (O) rich.

Referring now to FIG. 3, a deposition system 50 that may be utilized toform the N work function metal layer 32 in the gate stack 22 of theFinFET 10 of FIG. 1 is illustrated. In an embodiment, the depositionsystem 50 may receive precursor materials from a first precursordelivery system 52 and a second precursor delivery system 54. Theformation of the N work function metal layer 32 may be performed in adeposition chamber 56 that receives the first precursor material and thesecond precursor material.

The first precursor delivery system 52 and the second precursor deliverysystem 54 may work in conjunction with one another to supply the variousdifferent precursor materials to the deposition chamber 56. In anembodiment, the first precursor delivery system 52 may include a carriergas supply 58, a flow controller 60, and a precursor canister 62. Thecarrier gas supply 58 may supply a gas that may be used to help “carry”the precursor gas to the deposition chamber 56. The carrier gas may bean inert gas or other gas that does not react with the precursormaterial or other materials within the deposition system 50. Forexample, the carrier gas may be argon (Ar), helium (He), nitrogen (N₂),hydrogen (H₂), combinations of these, and so on, although any othersuitable carrier gas may alternatively be utilized. The carrier gassupply 58 may be a vessel, such as a gas storage tank, that is locatedeither locally to the deposition chamber 56 or else may be locatedremotely from the deposition chamber 56.

The carrier gas supply 58 may supply the desired carrier gas to the flowcontroller 60. The flow controller 60 may be utilized to control theflow of the carrier gas to the precursor canister 62 and, eventually, tothe deposition chamber 56, thereby also helping to control the pressurewithin the deposition chamber 56. The flow controller 60 may be, forexample, a proportional valve, a modulating valve, a needle valve, apressure regulator, a mass flow controller, combinations of these, andso on.

The flow controller 60 may supply the controlled carrier gas to theprecursor canister 62. The precursor canister 62 may be utilized tosupply a desired precursor to the deposition chamber 56 by vaporizing orsublimating precursor materials that may be delivered in either a solidor liquid phase. The precursor canister 62 may have a vapor region intowhich precursor material is driven into a gaseous phase so that thecarrier gas from the flow controller 60 may enter the precursor canister62 and pick-up or carry the gaseous precursor material out of theprecursor canister 62 and towards the deposition chamber 56.

The second precursor delivery system 54 may comprise components similarto the first precursor delivery system 52. Indeed, the second precursordelivery system 54 may comprise a second precursor material supplier 64,such as a gas storage tank or a machine to generate the second precursormaterial on an as-needed basis. The second precursor material supplier64 may supply a stream of the second precursor material to, for example,a flow controller 60 similar to the flow controller described above withrespect to the first precursor delivery system 52.

The flow controller 60 in the second precursor delivery system 54 mayhelp control the flow of the second precursor material to the precursorgas controller 66, and may be, for example, a proportional valve, amodulating valve, a needle vale, a pressure regulator, a mass flowcontroller, a combination of these, or the like, although any othersuitable method of controlling the flow of the second precursor materialmay alternatively be utilized. While not shown in FIG. 3, the secondprecursory delivery system 207 may also include a precursor canistersimilar to precursor canister 62 of the first precursor delivery system52.

The first precursor delivery system 52 and the second precursor deliverysystem 54 may supply their individual precursor materials into aprecursor gas controller 66 that connects and isolates the firstprecursor delivery system 52 and the second precursor delivery system 54from the deposition chamber 56 in order to deliver the desired precursormaterial to the deposition chamber 56. The precursor gas controller 66may include such devices as valves, flow meters, sensors, and the liketo control the delivery rates of each of the precursors, and may becontrolled by instructions received from a control unit 68.

The precursor gas controller 66, upon receiving instructions from thecontrol unit 68, may open and close valves so as to connect one of thefirst precursor delivery system 52 and the second precursor deliverysystem 54 to the deposition chamber 56. Such action directs a desiredprecursor material through a manifold 70, into the deposition chamber56, and to a gas dispenser 72, which could be a funnel or a showerhead(which are each shown in FIG. 3). The gas dispenser 72 may be utilizedto disperse the chosen precursor material into the deposition chamber 56and may be designed to evenly disperse the precursor material in orderto minimize undesired process conditions that may arise from unevendispersal. In an embodiment, the gas dispenser 72 has a circular designwith openings dispersed evenly to allow for the dispersal of the desiredprecursor material into the deposition chamber 56.

The deposition chamber 56 may receive the desired precursor materialsand expose the precursor materials to a wafer 74 having a plurality ofFinFETs with a partially formed gate stack 22 thereon. The depositionchamber 56 may be any desired shape that may be suitable for dispersingthe precursor materials and contacting the precursor materials with thepartially formed gate stack 22. In an embodiment, the deposition chamber56 has a cylindrical sidewall and corresponding circular bottom.Furthermore, the deposition chamber 56 may be surrounded by a housing 76made of material that is inert to the various process materials. In anembodiment, the housing 76 may be steel, stainless steel, nickel,aluminum, alloys of these, or combinations of these.

Within the deposition chamber 56 the wafer 74 may be placed on apedestal 78 (or other mounting platform) in order to position andcontrol the wafer 74 during the deposition process. The pedestal 221 mayinclude a heater 80 or other heating mechanism in order to heat thewafer 74 during the deposition process. In an embodiment, the heater 80in the pedestal 78 is spaced apart from the gas dispenser 72 (i.e., thefunnel or the showerhead) by about 50 mils to 150 mils. While a singlepedestal 78 is illustrated in FIG. 3, any number of pedestals 78 ormounting structures (with or without heaters) may additionally beincluded within the deposition chamber 56.

The deposition chamber 56 may also have an exhaust outlet 82 for exhaustgases to exit the deposition chamber 56. For example, an argon (Ar)purge gas may be removed from the deposition chamber 56 through theexhaust outlet 82. A vacuum pump 84 may be connected to the exhaustoutlet 82 of the deposition chamber 56 in order to help evacuate theexhaust gases. The vacuum pump 84, under control of the control unit 68,may also be utilized to reduce and control the pressure within thedeposition chamber 56 to a desired pressure. In an embodiment, thepressure within the deposition chamber 56 is maintained at about 2 Torrand about 5 Torr. The vacuum pump 84 may also be utilized to evacuateone precursor material from the deposition chamber 56 in preparation forthe introduction of the next precursor material.

After the self-limiting reactions have finished, the deposition chamber56 may be purged of the precursor material therein. For example, thecontrol unit 68 may instruct the precursor gas controller 66 todisconnect the first precursor delivery system 52 (containing the firstprecursor material to be purged from the deposition chamber 56) and toconnect a purge gas delivery system 86 to deliver a purge gas to thedeposition chamber 56. In an embodiment the purge gas delivery system 86may be a gaseous tank or other facility that provides a purge gas suchas argon (Ar), nitrogen (N₂), xenon (Xe), or other non-reactive gas tothe deposition chamber 56. Additionally, the control unit 68 may alsoinitiate the vacuum pump 84 in order to apply a pressure differential tothe deposition chamber 56 to aid in the removal of the first precursormaterial.

The deposition system 50 of FIG. 3 may be utilized to form the N workfunction metal layer 32 in the gate stack 22 of the FinFET 10 of FIG. 1through an atomic layer deposition (ALD) process. Referring now to FIG.4, an embodiment method 90 of forming the gate stack 22 for the FinFET10 is illustrated. In block 92, the wafer 74 (which has a plurality ofFinFETs each with a partially formed gate stack 22) is loaded into thedeposition chamber 56. Thereafter, in block 94, the wafer 74 is heatedusing the heater 80 in the pedestal 78. In an embodiment, the wafer 74is heated to a temperature of between about 350 degrees Celsius to about450 degrees Celsius.

In block 96, a first precursor of a tantalum pentachloride (TaCl₅) isintroduced or pulsed into the deposition chamber 56. In an embodiment,the first precursor is pulsed for between about 5 second to about 20seconds. Even so, the first precursor may be pulsed for a longer orshort time period. In an embodiment, the first precursor is transportedto the deposition chamber 56 using an argon (Ar) carrier gas with a flowrate of between about 500 standard cubic centimeters per minute (sccm)and about 1500 sccm. In an embodiment, the first precursor may be pulsedat about 70 degrees Celsius to about 100 degrees Celsius. Even so, thefirst precursor may be pulsed with another suitable flow rate andanother suitable temperature.

In block 98, the first precursor of the tantalum pentachloride (TaCl₅)is purged from the atomic layer deposition chamber. In an embodiment,the first precursor is purged for between about 2 second to about 10seconds. Even so, the first precursor may be purged for a longer orshort time period. In an embodiment, the first precursor is purged fromthe deposition chamber 56 using an argon (Ar) purge gas with a flow rateof between about 2500 standard cubic centimeters per minute (sccm) andabout 3500 sccm. Even so, the first precursor may be purged usinganother suitable gas with another suitable flow rate.

In block 100, a second precursor of triethylaluminum (Al(C₂H₅)₃) isintroduced or pulsed into the deposition chamber 56. In an embodiment,the second precursor is pulsed for between about 5 second to about 20seconds. Even so, the second precursor may be pulsed for a longer orshort time period. In an embodiment, the second precursor is transportedto the deposition chamber 56 using an argon (Ar) carrier gas with a flowrate of between about 500 standard cubic centimeters per minute (sccm)and about 1500 sccm. In an embodiment, the second precursor may bepulsed at about 25 degrees Celsius to about 45 degrees Celsius. Even so,the second precursor may be pulsed with another suitable flow rate andanother suitable temperature.

In block 102, the second precursor of the triethylaluminum (Al(C₂H₅)₃)is purged from the deposition chamber 56. In an embodiment, the secondprecursor is purged for between about 2 second to about 10 seconds. Evenso, the second precursor may be purged for a longer or short timeperiod. In an embodiment, the first precursor is purged from thedeposition chamber 56 using an argon (Ar) purge gas with a flow rate ofbetween about 2500 standard cubic centimeters per minute (sccm) andabout 3500 sccm. Even so, the second precursor may be purged usinganother suitable gas with another suitable flow rate.

With the second precursor purged, the N work function metal layer 32 forthe gate stack 22 is generated after a suitable opportunity foroxidation. As noted above, the N work function metal layer 32 hasoxidation layers 24 on opposing sides of the tantalum aluminide carbide(TaAlC) layer 36.

Referring now to FIG. 5, the process 104 of pulsing the first precursor106, purging the first precursor 108, pulsing the second precursor 110,and then purging the second precursor 112 may be repeated to formadditional monolayers of the tantalum aluminide carbide (TaAlC) layer36. Indeed, the arrow of FIG. 5 illustrates that the alternativepulsing/purging process, as described in detail above, may be repeated.Once a suitable number of monolayers of the tantalum aluminide carbide(TaAlC) layer 36 have been formed (e.g., nine layers, eleven layers,fifteen layers, and so on), the tantalum aluminide carbide (TaAlC) layer36 may be exposed to oxygen to permit oxidation to occur.

Referring now to FIG. 6, two different reaction models 114 are shown.Both TaC and TaAlC are formed in the reaction. However, at highertemperature the second reaction is more pronounced and more tantalumaluminide carbide (TaAlC) is formed. Thus, work function tuning can beachieved by tuning of process temperature effectively.

Referring now to FIG. 7, a chart 116 illustrating the effect oftemperature on a flat band voltage (V_(fb)) for a MOS capacitor havingan N work function metal layer formed from eleven monolayers isprovided. As shown, the flat band voltage changes from about −0.17 V toabout −0.39 V as the temperature is increased from about 350° C. toabout 400° C. when the N work function metal layer includes tantalumaluminide carbide (TaAlC) and a metal fill layer of tungsten (W) isused. For the purpose of reference, the chart 116 also includes the flatband voltage for a FinFET with the N work function metal layer oftantalum aluminide carbide (TaAlC) and a metal fill layer of aluminum(Al), which is labeled as N14 in the chart 116.

Referring now to FIG. 8, a chart 118 illustrating the effect ofthickness of the N work function metal layer is provided. As shown, theflat band voltage changes from about −0.25 V to about −0.38 V as thethickness of the N work function metal layer changes from 9 monolayers(9×) to about 15 monolayers (15×). Notably, the comparison of the flatband voltages at various thicknesses is made with a process temperatureof about 400° C.

Referring now to FIG. 9, a chart 120 illustrating the effect of aprecursor ratio on a flat band voltage (V_(fb)) for a FinFET having an Nwork function metal layer formed from eleven monolayers is provided. Asshown, the flat band voltage has a range of about −0.32 V to about −0.37V when the ratio of tantalum pentachloride (TaCl₅) to triethylaluminum(Al(C₂H₅)₃) used to form the aluminide carbide (TaAlC) layer of the Nwork function metal layer 32 is about 15 to 7. In addition, the flatband voltage has a range of about −0.35 V to about −0.40 V when theratio of tantalum pentachloride (TaCl₅) to triethylaluminum (Al(C₂H₅)₃)is about 10 to 10. The flat band voltage has a range of about −0.37 V toabout −0.43 V when the ratio of tantalum pentachloride (TaCl₅) totriethylaluminum (Al(C₂H₅)₃) is about 7 to 15.

Referring now to FIG. 10, a chart 122 depicting various parameters usedfor the tantalum aluminide carbide (TaAlC) layer 36 composition isprovided. As shown, the chart includes temperature ranges, precursorratios (labeled as the “condition”), the percentage of oxygen, thepercentage of aluminum, the percentage of chlorine, the percentage oftantalum, and the percentage of carbon. For reference, the percentagesof aluminum, tantalum, and carbon have been highlighted.

An embodiment fin field effect transistor (FinFET) including a finsupported by a semiconductor substrate, the fin extending between asource and a drain and having a channel region, and a gate stack formedover the channel region of the fin, the gate stack including an N workfunction metal layer comprising an oxidation layer on opposing sides ofa tantalum aluminide carbide (TaAlC) layer.

An embodiment method of forming a gate stack for a fin field effecttransistor (FinFET) including heating a wafer having the FinFET in anatomic layer deposition chamber, pulsing a first precursor of a tantalumpentachloride (TaCl₅) into the atomic layer deposition chamber with thewafer having the FinFET, purging the first precursor of the tantalumpentachloride (TaCl₅) from the atomic layer deposition chamber, pulsinga second precursor of triethylaluminum (Al(C₂H₅)₃) into the atomic layerdeposition chamber with the wafer having the FinFET, and purging thesecond precursor of the triethylaluminum (Al(C₂H₅)₃) from the atomiclayer deposition chamber with the wafer having the FinFET to generate anN work function metal layer for the gate stack, the N work functionmetal layer comprising a tantalum aluminide carbide (TaAlC) layer withan oxidation layer on opposing sides thereof.

An embodiment N metal work function composition for a gate stack of afin field effect transistor (FinFET) including aluminum in a range ofbetween about 16% to about 25%, carbon in a range of between about 20%to about 29%, tantalum in a range of between about 9% to about 16%, andoxygen in a range of between about 35% to about 50%.

While the disclosure provides illustrative embodiments, this descriptionis not intended to be construed in a limiting sense. Variousmodifications and combinations of the illustrative embodiments, as wellas other embodiments, will be apparent to persons skilled in the artupon reference to the description. It is therefore intended that theappended claims encompass any such modifications or embodiments.

What is claimed is:
 1. An N metal work function composition comprising:a gate stack of a transistor, the gate stack comprising: a first TaAlCOmaterial layer, the first TaAlCO layer comprising: aluminum in a rangeof between about 16% to about 25%; carbon in a range of between about20% to about 29%; tantalum in a range of between about 9% to about 16%;and oxygen in a range of between about 35% to about 50%; a TaAlC layerover the first TaAlCO material layer; and a second TaAlCO material layerover the TaAlC layer.
 2. The N metal work function composition of claim1, wherein the first TaAlCO material layer, the TaAlC layer, and thesecond TaAlCO material layer collectively form an N metal work functionlayer.
 3. The N metal work function composition of claim 2, wherein athickness of the N metal work function layer is between about 30 toabout 90 angstroms.
 4. The N metal work function composition of claim 3,wherein a ratio of the aluminum to the carbon is about 0.5 to about 1.3,a ratio of the tantalum to the carbon is about 0.2 to about 0.8, and aratio of the aluminum to the tantalum is about 1 to about 3.6.
 5. The Nmetal work function composition of claim 1, wherein the TaAlC layerprovides a tunable work function.
 6. The N metal work functioncomposition of claim 5, wherein the tunable work function is tunable byvarying a process temperature used in forming the TaAlC layer.
 7. The Nmetal work function composition of claim 1, wherein the TaAlC layercomprises a plurality of monolayers.
 8. The N metal composition of claim1, wherein the TaAlC layer has a U-shape.
 9. An N metal work functioncomposition comprising: a fin extending from a substrate; a gateelectrode extending over a channel region of the fin, the gate electrodehaving spacers along sidewalls of the gate electrode, the gate electrodecomprising: a first gate dielectric layer, the first gate dielectriclayer extending along sidewalls of the spacers; a second gate dielectriclayer over the first gate dielectric layer along the sidewalls of thespacers; an N metal work function layer; and a metal fill layer over theN metal work function layer; wherein the N metal work function layercomprises a first metal layer having a first oxide layer and a secondoxide layer along opposing surfaces such that the first metal layer isbetween the first oxide layer and the second oxide layer, the firstoxide layer and the second oxide layer comprising: aluminum in a rangeof between about 16% to about 25%; carbon in a range of between about20% to about 29%; tantalum in a range of between about 9% to about 16%;and oxygen in a range of between about 35% to about 50%; and wherein aratio of the aluminum to the carbon is about 0.5 to about 1.3, a ratioof the tantalum to the carbon is about 0.2 to about 0.8, and a ratio ofthe aluminum to the tantalum is about 1 to about 3.6.
 10. The N metalwork function composition of claim 9, wherein the first metal layercomprises monolayers of a tantalum aluminide carbide (TaAlC).
 11. The Nmetal work function composition of claim 10, wherein oxygen reacts withthe TaAlC to form the first oxide layer and the second oxide layer on atleast one of the monolayers of the tantalum aluminide carbide (TaAlC).12. The N metal work function composition of claim 9, wherein athickness of the N metal work function layer is between about 30 toabout 90 angstroms.
 13. The N metal work function composition of claim9, wherein the first metal layer comprises TaAlC.
 14. The N metal workfunction composition of claim 9, wherein the first oxide layer and thesecond oxide layer comprises TaAlCO.
 15. An N metal work functioncomposition comprising: a U-shaped N metal work function layer over achannel region of a fin, the U-shaped N metal work function layercomprising a first TaAlCO layer, a second a TaAlCO layer, and TaAlClayer interposed between the first TaAlCO layer and the second TaAlCOlayer, the first TaAlCO layer and the second TaAlCO layer comprising:aluminum in a range of between about 16% to about 25%; carbon in a rangeof between about 20% to about 29%; tantalum in a range of between about9% to about 16%; and oxygen in a range of between about 35% to about50%; and a metal fill over the U-shaped N metal work function layer. 16.The N metal work function composition of claim 15, wherein a thicknessof the U-shaped N metal work function layer is between about 30 to about90 angstroms.
 17. The N metal work function composition of claim 15,wherein a ratio of the aluminum to the carbon is about 0.5 to about 1.3,a ratio of the tantalum to the carbon is about 0.2 to about 0.8, and aratio of the aluminum to the tantalum is about 1 to about 3.6.
 18. The Nmetal work function composition of claim 15, wherein the TaAlC layerprovides a tunable work function.
 19. The N metal work functioncomposition of claim 15, wherein the TaAlC layer comprises a pluralityof monolayers.
 20. The N metal work function composition of claim 15,wherein a ratio of the aluminum to the carbon is about 0.5 to about 1.3,a ratio of the tantalum to the carbon is about 0.2 to about 0.8, and aratio of the aluminum to the tantalum is about 1 to about 3.6, andwherein the TaAlC layer comprises a plurality of monolayers.